Method and device for determining a data configuration of a digital signal of an image

ABSTRACT

The invention relates to a method of determining a data configuration of a digital signal of an image, the signal having undergone at least one spatio-temporal transformation in at least one resolution level, characterized in that the method comprises the following steps:  
     determining at least one minimum rate reduction (D min ) with respect to the total data rate of at least one resolution level of the signal, as a function of a quality mode desired for the signal,  
     configuring the data of the signal in at least one quality layer defined for at least one resolution level of the signal such that said at least one quality layer so defined corresponds to a given visual quality of the signal, the data making up that at least one quality layer being obtained by a reduction (D) of the total rate of the data of said at least one resolution level of the signal which is greater than or equal to the minimum reduction (D min ).

[0001] The invention relates to a method and a device for determining adata configuration of a digital signal of an image conveying a totaldata rate D_(t).

[0002] Currently, it is known that digital cameras provide a pluralityof compression modes for image signals in accordance with the JPEGstandard which each correspond to a given image quality mode.

[0003] For example, in its digital cameras the Canon corporationprovides the quality modes termed “Super Fine”, “Fine” and “Normal”which are characterized by quantization tables used on encoding. Thus,the values of the quantization tables used for the “Normal” mode arehigher than for the other modes and result in an approximation of animage which is less fine, but also with a higher level of compression.

[0004] These quantization tables are comparable to the default tablesdefined in the JPEG standard with a respective quality parameter of 97,93 and 73.

[0005] Thus the use of such encoding parameters makes it possible toobtain quantization tables which characterize quality modes which aresimilar to the aforementioned modes.

[0006] According to the JPEG standard, the desired quality mode ischosen definitively before the encoding of the image signal and it isnot possible later to pass to another quality mode for the encoded imagesignal.

[0007] A rate/distortion allocation method is known which makes itpossible to obtain an image signal in accordance with the JPEG2000standard and which enables quality layers to be constructedcorresponding to a target rate solely for the maximum resolution.

[0008] The objective of the rate/distortion allocation method commonlyused in implementations of the JPEG2000 standard (JJ2000http://jj2000.epfl.ch, kakadu www.kakadusoftware.com, or Jasperhttp://www.ece.uvic.ca/˜mdadams/jasper/) is to obtain a target ratewhile minimizing the distortion of an image. That method relies on analgorithm which is described in the article entitled “High performancescalable image compression with EBCOT” by D. Taubman, which appeared in“IEEE Transactions on image processing”, Vol. 9, N^(o) 7, Jul. 2000,pages 1158 to 1170.

[0009] For each block of coefficients B_(i) of the image signaldecomposed into frequency sub-bands at a plurality of resolution levels,it is possible to determine a plurality of truncation points R^(n) ofthe bitstream of the block B_(i) corresponding respectively to adistortion D_(i) ^(n). The objective of this method is to optimize thepoints (R_(i) ^(n),D_(i) ^(n)) in order to minimize the total distortion$D = {\sum\limits_{i}D_{i}^{n_{i}}}$

[0010] of the image with a rate constraint${R = {{\sum\limits_{i}R_{i}^{n_{i}}} \leq R_{\max}}},$

[0011] n_(i) being the truncation point selected for the block i. Thisamounts to finding the smallest value of λ such that R(λ)≦R^(max) andwhich minimizes the equation$\left( {{D(\lambda)} + {\lambda \quad {R(\lambda)}}} \right) = {\sum\limits_{i}{\left( {D_{i}^{n_{i}} + {\lambda \quad R_{i}^{n_{i}}}} \right).}}$

[0012] For this, the following steps may be taken:

[0013] Initialization of the extreme values λ_(min) and λ_(max),

[0014] Setting a value λ equal to$\frac{\lambda_{\min} + \lambda_{\max}}{2},$

[0015] Determining, for that value λ, the truncation points for all theblocks B_(i) which minimize the equation${\left( {{D(\lambda)} + {\lambda \quad {R(\lambda)}}} \right) = {\sum\limits_{i}\left( {D_{i}^{n_{i}} + {\lambda \quad R_{i}^{n_{i}}}} \right)}},$

[0016] If R(λ)>R^(max), setting λ_(min)=λ, otherwise setting λ_(max)=λand looping back to the second step.

[0017] For each value of λ tested, the calculations must thus be redoneconsidering all the blocks of the image, which may prove costly in termsof calculations and thus in execution time.

[0018] Furthermore, the allocation of rate is calculated solely for themaximum resolution level in the image signal.

[0019] From the document EP 1 158 764 A2 there is also known a method ofencoding an image signal in accordance with the JPEG 2000 standard andan associated method of analyzing these images in order to free upmemory.

[0020] The encoding method makes it possible to obtain a JPEG2000 filestructure with multiple quality layers for each resolution. Beforedeleting data in order to free up memory, a method of analyzing andcalculating is necessary in order to determine how many quality layerswill be deleted to obtain the desired reduction in rate.

[0021] It should be noted that these steps of analyzing and calculatingthe data are repeated each time it is desired to free up memory, whichproves to be disadvantageous.

[0022] The object of the present invention is to remedy at least one ofthe aforementioned drawbacks by providing a method of determining a dataconfiguration of a digital signal of an image, the signal havingundergone at least one spatio-temporal transformation in at least oneresolution level, characterized in that the method comprises thefollowing steps:

[0023] determining at least one minimum rate reduction D_(min) withrespect to the total data rate of at least one resolution level of thesignal, as a function of a quality mode desired for the signal,

[0024] configuring the data of the signal in at least one quality layerdefined for at least one resolution level of the signal such that eachquality layer so defined corresponds to a given visual quality of thesignal, the data making up that at least one quality layer beingobtained by a reduction D in the total rate of the data of said at leastone resolution level of the signal which is greater than or equal to theminimum reduction D_(min).

[0025] In a complementary manner, the invention also relates to a devicefor determining a data configuration of a digital signal of an image,the signal having undergone at least one spatio-temporal transformationin at least one resolution level, characterized in that the devicecomprises:

[0026] means for determining at least one minimum rate reduction D_(min)with respect to the total data rate of at least one resolution level ofthe signal, as a function of a quality mode desired for the signal,

[0027] means for configuring the data of the signal in at least onequality layer defined for at least one resolution level of the signalsuch that said at least one quality layer so defined corresponds to agiven visual quality of the signal, the data making up that at least onequality layer being obtained by a reduction D of the total rate of thedata of said at least one resolution level of the signal which isgreater than or equal to the minimum reduction D_(min).

[0028] So configured, the image signal may be transmitted as it is to acommunication apparatus where a user receiving that signal may, if sodesired, delete the data of the signal so enabling him to keep only dataof interest, i.e. those making up the quality layer or layers definedpreviously for one or more resolution levels.

[0029] A signal will thus be obtained which is configured to the desiredquality mode, to the desired resolution, and with a given visualquality, which was not possible with the prior art.

[0030] The user may even delete one or more quality layers of theconfigured signal to keep only the one or ones of interest.

[0031] It should be noted that if a quality layer is defined for aresolution other than the maximum resolution, the determination of thereduction in rate is performed with respect to the total data rate forthat other resolution.

[0032] Moreover, if a plurality of quality layers are defined, aplurality of corresponding determinations of minimum rate reduction willbe necessary.

[0033] Before transmitting the signal having the desired configurationit may also be envisaged to delete the above-mentioned data from thatsignal.

[0034] That converted signal may then be transmitted or not to a remotecommunication apparatus.

[0035] It is also possible for the method according to the invention tobe performed in a communication apparatus where intervention by a useris involved.

[0036] Furthermore, the invention does not require complex calculationswhich give rise to a long time of execution, by contrast to the priorart.

[0037] This is advantageous when the equipment in which the signal isconfigured has a relatively reduced computational capacity.

[0038] In addition, when the signal is configured in accordance with theinvention, that is to say when one or more quality layers correspondingto a given visual quality have been created, it is not necessarythereafter to carry out calculations on the data of the signal in orderto know which are to be deleted in order to free up memory space.

[0039] This is because the quality layer or layers have been expresslycreated in order to give the user the possibility later of converting animage signal from one given quality mode to a lower quality mode withoutadditional calculation.

[0040] The configuration of the data of the signal according to theinvention may give rise to the creation of a single quality layer for asingle resolution level, or to a quality layer per resolution levelconcerned for a plurality of resolution levels, or even for eachresolution level of the signal.

[0041] Thus the reduction in rate making it possible to obtain thequality mode desired while preserving a given visual quality may be seenas the deletion of data corresponding to a quality level hierarchicallyabove to attain the quality level created hierarchically below.

[0042] According to the invention it is also possible to consider that aplurality of hierarchical quality layers are created for a singleresolution level or a plurality of layers per resolution level for aplurality of resolution levels, each quality layer corresponding to agiven visual quality.

[0043] The deletion, for example, of a quality level hierarchicallyabove is accompanied by a reduction in the rate at least equal to aminimum value and thus makes it possible to obtain the desired qualitymode with the guarantee of a given visual quality.

[0044] According to one feature, the signal issuing from said at leastone spatio-temporal transformation comprises blocks each containing atleast one transformed coefficient having the form of a series of binaryelements, the data making up a quality layer which is defined in atleast one resolution level of the signal, corresponding, for at leastone block of a given resolution level, to at least a number n ofportions of binary elements of said at least one block.

[0045] The number n obtained thus makes it possible to ensure the lackof visual artifacts in the image signal.

[0046] According to another feature, said at least one number n ofportions of binary elements is determined as a function of a givennumber N which corresponds to the maximum number of portions of binaryelements which it is possible to delete in a block to obtain a givenvisual quality in the resolution considered.

[0047] The threshold N thus makes it possible to ensure that by creatinga quality layer in a given resolution level of the signal, that signaldoes not risk having its visual quality degraded by the deletion ofcorresponding data.

[0048] According to another feature, the method comprises a step ofclassifying the data blocks as a function of the values of thedistortion which is generated for each block when the maximum givennumber N of portions of binary elements is deleted from each block.

[0049] According to another feature, the data blocks are classified intodifferent classes of blocks to each of which belong the data blockshaving given rise to values of distortion which are consistent with eachother.

[0050] Each of these classes has statistical properties which areequivalent in terms of the ratio standard deviation/mean.

[0051] The classification of the blocks into different classes as afunction of the distortion values makes it possible to adapt, for eachblock, the number of portions of binary elements to delete with respectto the aforementioned maximum level N as a function of theclassification of that block.

[0052] Thus, within the same resolution level, it is possible todistribute the reduction in rate taking into account the classificationof the blocks and, for example, to decide to delete more binary portionsfor certain blocks than for others.

[0053] It is for example preferable to delete more portions of binaryelements for a block put in a class in which the distortion generated isthe least.

[0054] Conversely, for the blocks generating greater distortion, asmaller number of portions of binary elements will be deleted for theblocks of that class.

[0055] According to one feature, the signal issuing from said at leastone spatio-temporal transformation comprises transformed coefficientsgrouped into blocks in which each coefficient is quantized over aplurality of bits, each bitplane of a block being encoded by a pluralityof encoding passes which each provides a portion of the encoding datafor the block considered, configuring the data of the signal in at leastone quality layer comprising obtaining, in at least one resolution levelof the signal and for each of the blocks considered, a minimum number mof encoding passes corresponding to the given visual quality.

[0056] According to another feature, the minimum number m is obtained asa function of a maximum given number N of encoding passes which it ispossible to delete for the coefficients of a data block in order toobtain a given visual quality in the resolution considered.

[0057] According to another feature, the invention relates to a methodof determining a data configuration of a digital signal of an image, thesignal having undergone at least one spatio-temporal transformation inat least one resolution level, characterized in that the methodcomprises the following steps:

[0058] determining at least one minimum rate reduction D_(min) withrespect to the total data rate of at least one resolution level of thesignal, as a function of a quality mode desired for the signal,

[0059] distributing, over at least certain of the resolution levels ofthe signal, a rate reduction D greater than or equal to D_(min) andwhich is such that the reduction in data rate distributed in eachresolution level is less than or equal to a threshold representing agiven visual quality.

[0060] In a complementary manner, the invention also relates to a devicefor determining a data configuration of a digital signal of an image,the signal having undergone at least one spatio-temporal transformationin at least one resolution level, characterized in that the devicecomprises:

[0061] means for determining at least one minimum rate reduction D_(min)with respect to the total data rate of at least one resolution level ofthe signal, as a function of a quality mode desired for the signal,

[0062] means for distributing, over at least certain of the resolutionlevels of the signal, a rate reduction D greater than or equal toD_(min) and which is such that the reduction in data rate distributed ineach resolution level is less than or equal to a threshold representinga given visual quality.

[0063] According to this feature, as a function of the quality mode fora given resolution level which it is desired to propose to the user andthus of a minimum reduction in data rate, the reduction in rate enablingthat quality mode to be obtained will be distributed in differentresolution levels, while ensuring that the given visual quality in thegiven resolution level is not affected.

[0064] The distribution of the rate reduction will be made by deleting,for a given quality layer, encoding passes in the differentaforementioned resolution levels, thus achieving a configuration of thedata of the signal.

[0065] According to still another feature, the invention relates to amethod of determining a data configuration of a digital signal of animage, the signal having undergone at least one spatio-temporaltransformation in at least one resolution level, thus providingtransformed coefficients each taking the form of a series of binaryelements comprising a plurality of portions, characterized in that themethod comprises the following steps:

[0066] i) determining at least one minimum rate reduction D_(min) withrespect to the total data rate of at least one resolution level of thesignal, as a function of a quality mode desired for the signal,

[0067] ii) determining, for a given resolution level R=R_(i) and for atleast certain transformed coefficients of that level, a number m whichmay vary from one coefficient to another, of portions of binary elementsto delete from the signal, with m≦N, where N is a maximum given numberwhich guarantees a given visual quality in the resolution levelconsidered,

[0068] iii) determining the reduction in rate D_(i) generated by thedeletion in the resolution level R of the m portions of binary elementsof said at least certain transformed coefficients,

[0069] iv) comparing the rate reduction added to the possible ratereduction determined for the resolution level hierarchically above withrespect to the minimum rate reduction D_(min),

[0070] v) as a function of the result of the comparison, deciding as tothe reiteration of steps ii) to v) for the resolution level R or for theresolution level below R=R_(i-1) or as to the determined dataconfiguration.

[0071] In a complementary manner, the invention relates to a device fordetermining a data configuration of a digital signal of an image, thesignal having undergone at least one spatio-temporal transformation inat least one resolution level, thus providing transformed coefficientseach taking the form of a series of binary elements comprising aplurality of portions, characterized in that the device comprises:

[0072] means for determining at least one minimum rate reduction D_(min)with respect to the total rate of data of at least one resolution levelof the signal, as a function of a quality mode desired for the signal,

[0073] means for determining, for a given resolution level R=R_(i) andfor at least certain transformed coefficients of that level, a number m,which may vary from one coefficient to another, of portions of binaryelements to delete from the signal, with m≦N, where N is a maximum givennumber which guarantees a given visual quality in the resolution levelconsidered,

[0074] means for determining the reduction in rate D_(i) generated bythe deletion in the resolution level R of the m portions of binaryelements of said at least certain transformed coefficients,

[0075] means for comparing the rate reduction added to the possible ratereduction determined for the resolution level hierarchically above withrespect to the minimum rate reduction D_(min),

[0076] means for deciding as to the determined configuration of thedata, as a function of the result of the comparison.

[0077] The invention thus proceeds iteratively commencing with the upperresolution levels and, at each resolution level, by searching for thenumber of portions of binary elements which can be deleted from thequality layer being processed in order to obtain a sufficient ratereduction, while ensuring that this number is always less than or equalto a threshold.

[0078] This threshold guarantees a given visual quality and is there toensure that the deletion of a quantity of data from the signal in agiven resolution level does not risk giving rise to a degradation in thevisual quality of the signal obtained further to the deletion.

[0079] For a resolution level, once a number of portions of binaryelements to delete has been found which respects the given visualquality criterion and which gives rise to a sufficient reduction inrate, the configuration of the signal is determined for that resolutionlevel.

[0080] It will be noted that the determination of a data configurationof a digital signal according to the invention makes it possible in away to structure the signal into portions of data which are defined insuch a manner as to satisfy a given visual quality criterion.

[0081] The signal so configured in accordance with the invention has ahierarchical structure of the data in terms of quality corresponding tothose portions of data.

[0082] It will be noted that the given visual quality corresponds to avisual quality of a non-degraded image signal, that is to say to animage signal having no visible artifacts.

[0083] According to a supplementary feature, the invention relates to amethod of determining a data configuration of a digital signal of animage, the signal having undergone at least one spatio-temporaltransformation in at least one resolution level, thus providingtransformed coefficients each taking the form of a series of binaryelements comprising a plurality of portions, characterized in that themethod comprises the following steps:

[0084] i) determining at least one minimum rate reduction D_(min) withrespect to the total rate of at least one given display resolution levelR_(a) as a function of a quality mode desired for the signal,

[0085] ii) determining, for a resolution level R_(i) which correspondsinitially to R_(a) and for at least certain transformed coefficients ofthat level, a number m, which may vary from one coefficient to another,of portions of binary elements to delete from the signal, with m≦N,where N is a maximum given number which guarantees a given visualquality in the resolution level considered,

[0086] iii) determining the reduction in rate D_(i) generated by thedeletion in the resolution level Ri of the m portions of binary elementsof said at least certain transformed coefficients,

[0087] iv) comparing the reduction in rate with respect to the minimumrate reduction D_(min),

[0088] v) as a function of the result of the comparison, deciding as tothe reiteration of steps ii) to v) for the resolution level R_(i) or forthe resolution level hierarchically below R_(i)=R_(i)−1 or as to thereiteration of steps i) to v) for the level of display resolutionhierarchically below R_(a)=R_(a)−1 or as to the determined dataconfiguration.

[0089] In a complementary manner, the invention relates to a device fordetermining a data configuration of a digital signal of an image, thesignal having undergone at least one spatio-temporal transformation inat least one resolution level, thus providing transformed coefficientseach taking the form of a series of binary elements comprising aplurality of portions, characterized in that the device comprises:

[0090] means for determining at least one minimum rate reduction D_(min)with respect to the total rate of at least one given display resolutionlevel R_(a)=R_(i) as a function of a quality mode desired for thesignal,

[0091] means for determining, for a resolution level R_(i) whichcorresponds initially to R_(a) and for at least certain transformedcoefficients of that level, a number m which may vary from onecoefficient to another, of portions of binary elements to delete fromthe signal, with m≦N, where N is a maximum given number which guaranteesa given visual quality in the resolution level considered,

[0092] means for determining the reduction in rate D_(i) generated bythe deletion in the resolution level R_(i) of the m portions of binaryelements of said at least certain transformed coefficients,

[0093] means for comparing the reduction in rate with respect to theminimum rate reduction D_(min),

[0094] means for deciding as to the configuration of the data, as afunction of the result of the comparison.

[0095] According to this feature, a minimum reduction in rate isdetermined with respect to the total data rate of the current resolutionlevel and not solely with respect to the total data rate of the maximumresolution level.

[0096] Thus a data configuration is defined corresponding to the givenquality mode in the current resolution level and in all the resolutionlevels below.

[0097] In this manner, it is ensured that in each of those resolutionlevels, the quality layer created satisfies the given quality mode.

[0098] The invention also concerns a digital camera comprising a deviceas briefly disclosed above.

[0099] According to another aspect, the invention also relates to:

[0100] an information storage means which can be read by a computer or amicroprocessor comprising code instructions for a computer program forexecuting the steps of the method according to the invention as for theone briefly set out above, and

[0101] a partially or totally removable information storage means whichcan be read by a computer or a microprocessor containing codeinstructions of a computer program for executing the steps of the methodaccording to the invention as for the one briefly disclosed above.

[0102] According to yet another aspect, the invention relates to acomputer program which can be loaded into a programmable apparatus,containing sequences of instructions or portions of software code forimplementing the steps of the method according to the invention asbriefly disclosed above, when said computer program is loaded andexecuted on the programmable apparatus.

[0103] As the features and advantages relating to the device, to thedigital camera comprising such a device, to the information storagemeans and to the computer program are the same as those disclosed aboveconcerning the method according to the invention, they will not berepeated here.

[0104] Other features and advantages of the present invention willemerge more clearly from a reading of the following description, givenwith reference to the accompanying drawings, in which:

[0105]FIG. 1 is a diagram of a system for encoding a digital signal ofan image in which the invention is implemented;

[0106]FIG. 2 is a diagram of a programmable apparatus implementing theinvention;

[0107]FIG. 3a is a diagram of a digital image output from the imagesource 1 of FIG. 1;

[0108]FIG. 3b is a diagram of the image of FIG. 3a after having beentransformed by the circuit 21 of FIG. 1;

[0109]FIG. 4 is a diagram of the representation of the bitplanes of thecoefficients of a data block B_(i);

[0110]FIG. 5a is a diagram of the different steps of forming an imagesignal configured according to the invention;

[0111]FIG. 5b is a diagram of the different steps of transcoding animage signal configured according to the invention;

[0112]FIG. 6a is an algorithm for determining a configuration of data ofa digital signal of an image according to the invention;

[0113]FIG. 6b is an algorithm detailing the operations carried out atstep S220 of the algorithm of FIG. 6a;

[0114]FIG. 7 shows the possible conversions from one quality mode toanother, as well as the corresponding rate reductions;

[0115]FIG. 8 illustrates the configuration of an image signal obtainedby implementation of the algorithms of FIGS. 6a and 6 b;

[0116]FIGS. 9a and 9 b illustrate the deletion of a resolution level inan image signal configured by the algorithm of FIGS. 6a and 6 b;

[0117]FIG. 10 represents an algorithm for configuring data of an imagesignal according to a variant form of the invention;

[0118]FIG. 11 illustrates a configuration of an image signal obtainedthrough applying the algorithm of FIG. 10;

[0119]FIG. 12 illustrates another configuration of the data of an imagesignal obtained through applying the algorithm of FIG. 10;

[0120]FIGS. 13a and 13 b illustrate the deletion of a resolution levelin an image signal configured by the algorithm of FIG. 10;

[0121]FIGS. 14a and 14 b respectively illustrate two possibleconfigurations of an image signal by implementation of the invention.

[0122] According to a chosen embodiment shown in FIG. 1, a system forencoding or compressing data is a system which comprises an input 20 towhich a source 1 of non-encoded data is connected.

[0123] The source 1 comprises for example a memory means, such as arandom access memory, a hard disk, a diskette or a compact disc, forstoring non-encoded data, this memory means being associated with asuitable reading means for reading the data therein. A means forrecording the data in the memory means can also be provided.

[0124] It will be considered more particularly hereinafter that the datato be encoded are a series of original digital samples representingphysical quantities and representing, for example, an image IM.

[0125] The source 1 supplies a digital image signal IM to the input ofthe encoding circuit 2. The image signal IM is a series of digitalwords, for example bytes. Each byte value represents a pixel of theimage IM, here with 256 levels of gray, or black and white image. Theimage can be a multispectral image, for example a color image havingcomponents in three frequency bands, of the red-green-blue or luminanceand chrominance type. Either the color image is processed in itsentirety, or each component is processed in a similar manner to themonospectral image.

[0126] It will also be noted that the image may be a fixed image (e.g. aphotograph) or an image from a video sequence.

[0127] Means 3 for exploiting encoded or compressed data are connectedat the output 25 of the encoding system 2.

[0128] The using means 3 comprises for example means of storing encodeddata, and/or means of transmitting encoded data.

[0129] The encoding system 2 conventionally comprises, starting from theinput 20, a spatio-temporal transformation unit 21 which may perform oneor more spatio-temporal transformations. For example, the circuit 21 mayperform decompositions into frequency sub-band signals of the datasignal, so as to carry out an analysis of that signal.

[0130] The transformation circuit 21 may possibly be connected to aquantization circuit 22. The quantization circuit performs aquantization which is known per se, for example a scalar quantization,or a vector quantization, of the coefficients, or groups ofcoefficients, of the frequency sub-band signals supplied by the circuit21.

[0131] The circuit 22 is connected to an entropy encoding circuit 23,which performs an entropy encoding, for example a Huffman encoding, oran arithmetic encoding, of the data quantized by the circuit 22.

[0132] Circuit 23 is connected to a device 24 which configures the data,for example quantized, of the transformed signal in order to create inthe signal one or more quality layers for one or more resolution levels(if the signal has a plurality of resolution levels).

[0133] The quality layer or layers are created while ensuring that eachquality layer created gives a specific visual quality.

[0134] This visual quality may be set in advance, for exampleempirically on the basis of a number of images of different nature whichare sufficiently homogeneous to be representative of the images which itis possible to encounter in practice. This visual quality may also takeinto account the signal considered.

[0135] Each quality layer corresponds to supplementary data which permita finer approximation of the signal. It may be decided to delete thehigher quality layers in order to reduce the rate of the signal andthus, on later decoding, a less fine reconstitution of the signal willbe achieved.

[0136] That quality layer or layers are thus determined in order for thereduction in rate considered from the total rate of data conveyed by theoriginal signal or by a lower resolution level to be sufficient takinginto account the quality mode which it is desired to provide the touser.

[0137] In the description which follows, three quality modes will beconsidered that are defined by the JPEG standard and, more particularly,that are characterized by default quantization tables defined in thatstandard with a respective quality parameter of 97, 93 and 73.

[0138] These quantization tables are comparable to those defining thequality modes “Super Fine”, “Fine”, and “Normal” of the cameras of theCanon corporation and thus define quality modes similar to those of theaforementioned cameras.

[0139] In the following description, the quality modes defined by theJPEG standard will, by analogy, be termed “Super Fine”, “Fine” and“Normal”, even though they are not strictly identical to the qualitymodes of the same name of the Canon cameras.

[0140] Generally, a minimum rate reduction D_(min) is fixed as afunction of the total rate of the given resolution and of the qualitymode to provide to the user.

[0141] In this manner, it is ensured that when a quality layer isconfigured in the signal, it will provide a visual quality which issatisfactory for one or more given criteria when the signal is reducedto that quality layer in the resolution considered.

[0142] It should be noted that a quality layer is constructed for agiven resolution.

[0143] If it is desired that the quality mode be available in the lowerresolutions, a quality layer must be constructed per resolutionconcerned, by calculating the reduction in rate with respect to thetotal rate for the resolution concerned and not for the entire signal.

[0144] Furthermore, as that layer will be created so as to correspond toa satisfactory reduction in rate D (D≧D_(min)) it will thus be ensuredthat the desired quality mode will be obtained.

[0145] It should be noted that it is possible, for a given resolution ofthe signal, just to create a quality layer while ensuring solely that itcorresponds to a satisfactory reduction in rate D, without botheringabout the visual quality obtained for the quality layer so created.

[0146] In that case, it is very probable that when the signal will laterbe reduced to that quality layer in that resolution, the visual qualityof the image obtained will be strongly degraded.

[0147] The invention makes it possible to avoid such an occurrence.

[0148] It should be noted that the signal configured according to theinvention and encoded may be exploited by the user who can then decideto convert the original quality mode of that signal into a lower qualitymode given the quality layer or layers created by the device 24, bydeleting one or more higher quality layers. The user could also deleteone or more resolution levels of the signal if desired.

[0149] Both conversions can be envisaged whether separately or incombination.

[0150] Moreover, it may be envisaged for the signal to be convertedbefore being transmitted to a remote user.

[0151] According to another approach, the configured and encoded signalmay be transmitted to a remote user who will then convert it, forexample, as indicated above.

[0152] With reference to FIG. 2, an example of a programmable apparatus100 implementing the invention is described. That apparatus is adaptedto configure the data of a digital signal of an image stored in theapparatus or in another communication apparatus.

[0153] The communication apparatus of FIG. 2 includes a device accordingto the invention, that is to say it possesses all the means necessaryfor the implementation of the different features of the invention (meansfor determining a minimum rate reduction, means for configuring thedata, means for distributing a rate reduction, means for determining anumber m, means for determining the rate reduction generated, means forcomparing, means for deciding), or itself constitutes such a deviceaccording to the invention.

[0154] The apparatus of FIG. 2 may thus comprise the encoding system 2of FIG. 1 including the device 24, or just the device 24.

[0155] According to the embodiment represented in FIG. 2, an apparatusimplementing the invention is, for example, a digital camera 100connected to different peripherals, for example a means for imageacquisition or storage.

[0156] The apparatus 100 of FIG. 2 comprises a communication bus 108 towhich are connected:

[0157] a central processing unit 120 (microprocessor),

[0158] a read-only memory 122, comprising a program “Progr” enabling theprogrammable apparatus to implement the invention (although a singleprogram is identified, it is possible to have a plurality of programs orsubprograms to implement the invention),

[0159] a random access memory 124, comprising registers adapted torecord variables modified during the execution of the aforementionedprogram,

[0160] a Flash (card) memory 126 for storing encoded images,

[0161] an image capturing circuit 128, for converting an optical imageinto a digital signal,

[0162] a color processing circuit 130, converting the digital signal andtransmitting it to the image memory 132,

[0163] a liquid crystal screen 134 making it possible to display animage stored in the Flash memory 126 or in the image memory 132,

[0164] a display control circuit 136, for controlling the display of theliquid crystal screen 134 under the control of the central processingunit 120,

[0165] switching means 138 (open/close switch, conversion mode switch,power switch, image selection switch, etc.) used by the user of thedigital camera,

[0166] an input port 140 for receiving an input signal from theswitches,

[0167] an interface cable 142 used to connect a host interface 144 ofthe camera to a corresponding digital camera interface of the hostcomputer 146. The cable 142 may for example be in accordance with theUSB (Universal Serial Bus) specification, and serves to transfer theimages contained in memory.

[0168] The communication bus 108 affords communication between thedifferent elements included in the apparatus 100 or connected to it. Therepresentation of the bus is non-limiting and, in particular, thecentral processing unit may possibly communicate instructions to anyelement of the apparatus 100 directly or by means of another element ofthe apparatus 100.

[0169] According to one variant, the memory 126 may contain data thatare compressed and stored, as well as the code of the invention (program“Progr”) which, once read by the apparatus 100, will be stored in thememory 124.

[0170] In a second variant, the program can be received via acommunication network in order to be stored in an identical fashion tothat described previously.

[0171] In general terms, an information storage means, which can be readby a computer or microprocessor, integrated or not into the apparatus,and which may possibly be removable, stores a program implementing themethod according to the invention

[0172] In more general terms, the program can be loaded into one of thestorage means of the apparatus 100 before being executed.

[0173] The central processing unit 120 will execute the instructionsrelating to the implementation of the invention, which are stored in theread only memory 122 or in the other storage elements. On powering up,the program or programs which are stored in a non-volatile memory, forexample the read-only memory 122, are transferred into the random accessmemory 124, which will then contain the executable code of theinvention, as well as registers for storing the variables necessary forimplementing the invention.

[0174] It should be noted that the communication apparatus capable ofimplementing the invention can also be a programmed apparatus.

[0175]FIG. 3a is a diagram of a digital image IM output from the imagesource 1 in FIG. 1.

[0176] This figure is decomposed by the transformation circuit 21 ofFIG. 1, which is a circuit for dyadic decomposition with threedecomposition levels.

[0177] The circuit 21 is, in this embodiment, a conventional set offilters, respectively associated with decimators by two, which filterthe image signal in two directions, into sub-band signals of high andlow spatial frequencies. The relationship between a high-pass filter anda low-pass filter is often determined by the conditions for perfectreconstruction of the signal. It should be noted that the vertical andhorizontal decomposition filters are not necessarily identical, althoughin practice this is generally the case. The circuit 21 comprises herethree successive analysis units for decomposing the image IM intosub-band signals according to three decomposition levels.

[0178] Generally, the resolution of a signal is the number of samplesper unit length used for representing that signal. In the case of animage signal, the resolution of a sub-band signal is related to thenumber of samples per unit length used for representing that sub-bandsignal horizontally and vertically. The resolution depends on the numberof decompositions made, the decimation factor and the initial imageresolution.

[0179] The first analysis unit receives the digital image signal IM and,in a known manner, delivers as an output four sub-band signals LL₃, LH₃,HL₃ and HH₃ with the highest resolution R₃ in the decomposition.

[0180] The sub-band signal LL₃ contains the components, or samples, oflow frequency, in both directions, of the image signal. The sub-bandsignal LH₃ comprises the image signal components of low frequency in afirst direction and of high frequency in a second direction. Thesub-band signal HL₃ comprises the components of high frequency in thefirst direction and the components of low frequency in the seconddirection. Finally, the sub-band signal HH₃ comprises the components ofhigh frequency in both directions.

[0181] Each sub-band signal is a set of real samples (which could alsobe integers) constructed from the original image, which containsinformation corresponding to a respectively vertical, horizontal anddiagonal orientation of the content of the image, in a given frequencyband. Each sub-band signal can be likened to an image.

[0182] The sub-band signal LL₃ is analyzed by an analysis unit similarto the previous one in order to supply four sub-band signals LL₂, LH₂,HL₂ and HH₂ of resolution level R₂.

[0183] Each of the sub-band signals of resolution R₂ also corresponds toan orientation in the image.

[0184] The sub-band signal LL₂ is analyzed by an analysis unit similarto the previous one in order to supply four sub-band signals LL₀ (byconvention), LH₁, HL₁, and HH₁, of resolution level R₁. It should benoted that the sub-band LL₀ by itself forms the resolution R₀.

[0185] Each of the sub-band signals of resolution R₁ also corresponds toan orientation in the image.

[0186]FIG. 3b represents the image IMD resulting from thespatio-temporal transformation applied to the image IM by the circuit21, into ten sub-bands and at 4 resolution levels: R₀ (LL₀), R₁(LL₂), R₂(LL₃), R₃ (original image). The image IMD contains as much informationas the original image IM, but the information is divided in frequency inthree decomposition levels.

[0187] Naturally the number of decomposition levels and consequently ofsub-bands can be chosen differently, for example 16 sub-bands over sixresolution levels, for a bi-dimensional signal such as an image. Thenumber of sub-bands per resolution level can also be different. Inaddition, it is possible for the decomposition not to be dyadic. Theanalysis and synthesis circuits are adapted to the dimension of thesignal processed.

[0188] In FIG. 3b the samples resulting from the transformation arestored sub-band by sub-band.

[0189] It will be noted that each sub-band of the image IMD ispartitioned into blocks Bi some of which are shown in FIG. 3b.

[0190] The circuits 22 and 23 of FIG. 1 apply independently to eachblock of each sub-band considered, the device 24 applying to all theblocks. The image signal encoded by the system 2 thus conveys blocks ofsamples obtained by the original encoding of the samples and whichconstitute the bitstream.

[0191] When the image signal is in accordance with the JPEG2000standard, these blocks of samples are known as code-blocks.

[0192] The encoded image signal also comprises a header.

[0193] This header comprises in particular the information relating tothe size of the image, i.e. its width and height, its position in acoordinate system, as well as the number of resolutions Rmax.

[0194] The size of the blocks for each sub-band at a given resolution isdetermined by two parameters signaled by markers in the bitstream of theimage signal in accordance with the JPEG2000 standard.

[0195] It will be noted that it is possible not to include in the signalthe blocks corresponding to at least one resolution level such as themaximum resolution level R₃ or even a plurality of upper resolutionlevels.

[0196] The deletion of a resolution level is accompanied by a two-foldreduction in the size of the image, which is advantageous in terms ofmemory space freed in order, for example, to store additional signals.

[0197] Such an advantage is particularly worthwhile for an apparatus oflimited memory capacity which stores digital images, such as a digitalcamera.

[0198] It should be noted that by keeping in the signal to be exploitedonly the blocks of lowest resolution level R₀ (low sub-band LL₀), it isnevertheless possible to obtain a good representation of the originalimage at a reduced scale.

[0199]FIG. 4 illustrates the entropy encoding by bitplanes of a datablock B_(i) of an image signal. Such progressive encoding is describedin the article entitled “High performance scalable image compressionwith EBCOT” by D. Taubman, which appeared in “IEEE Transactions on imageprocessing”, Vol. 9, N^(o). 7, July 2000, pages 1158 to 1170.

[0200] Each coefficient of a block B_(i) is a real number which isquantized over a plurality of bits (series of binary elements), forexample five bits in FIG. 4.

[0201] The bit plane PB₁ contains the MSB's (Most Significant Bits) ofthe coefficients of the block B_(i). The bit planes PB₂ to PB₅ containrespectively the bits that are less and less significant of thecoefficients of the block B_(i). The bit plane PB₅ thus contains theLSB's (Least Significant Bits) of the coefficients of the block B_(i).

[0202] Each bit plane is encoded in a plurality of encoding passes, forexample two. The result of the first encoding pass provides a part ofthe encoded data for the block in question, and the result of the secondpass provides another part of the encoded data comprising supplementarydetails.

[0203] In the final bitstream it may be chosen to include only a part ofthe data (portions of binary elements) corresponding to a whole numberof encoding passes: each encoding pass thus corresponds to a possibletruncation point of the bitstream for the block considered. With eachencoding pass there is associated a rate-distortion pair whichcorresponds to the supplementary rate and to the decrease in overalldistortion for the reconstructed image when the corresponding data whichhave just been encoded following the encoding pass considered areincluded in the final bitstream.

[0204] The rate/distortion allocation corresponds to the selection, foreach of the blocks of the image, of a truncation point of the dataT_(i)(R_(i) ^(n),D_(i) ^(n)) of the bitstream of the block B_(i), asindicated in FIG. 4.

[0205] Hierarchical quality layers or levels (“quality layers” in theJPEG2000 standard) may also be defined in the image signal. Each qualitylayer is defined by a whole number of supplementary encoding passes foreach block of the image, this number able to vary from one block toanother, and thus provides supplementary details for the decoding of theimage. It may for example be chosen to “coarsely” decode the image bytaking only the encoding passes corresponding to the first qualitylayer. According to the invention, the quality layers will beconstructed so as to correspond to the quality modes which the user canchoose.

[0206] The invention will make it possible to determine for each blockthe whole number of encoding passes defining each quality layer of thesignal, while preserving a given visual quality.

[0207] For an image signal in “Super Fine” quality mode which it may bedesired to convert into “Fine” or “Normal” mode, it is thus necessary todetermine, for each block, the truncation point corresponding to “SuperFine” mode, the truncation point corresponding to “Fine” mode and thetruncation point corresponding to “Normal” mode.

[0208]FIG. 5a is a diagram of the different steps of forming aconfigured signal, for example, an image signal in accordance with theJPEG2000 standard and which has three resolution levels R₀, R₁ and R₂.

[0209] As shown in that Figure, an original image signal IM isdecomposed into frequency sub-bands in at least one resolution levelduring a step S1 which applies a wavelet transform to it.

[0210] During that same step, the signal which has undergone, in theembodiment considered, several spatio-temporal transformations of theaforementioned type in a plurality of resolution levels, is subjected toquantization and entropy encoding operations in order to obtain a set ofencoded blocks of the image signal.

[0211] More particularly during the following step S2, the steps areimplemented which are illustrated in FIGS. 6a and 6 b of the system forconfiguring data according to the invention and described below.

[0212] During that step, provision is made, for each block ofcoefficients, to determine the truncation points necessary to configureor structure the final bitstream in order to obtain a set of qualitymodes guaranteeing a given visual quality, which will be accessible tothe final user.

[0213] During the following step S3, the final bitstream is constructedof the image signal in accordance with the JPEG2000 standard.

[0214]FIG. 5b illustrates the steps for the transcoding of an imagesignal in accordance with the JPEG2000 standard according to theinvention.

[0215] At the input there is an encoded image signal IM-JP2K inaccordance with the JPEG2000 standard which already has a certainstructure, in contrast to the unstructured image signal IM available atthe input at step S1 of FIG. 5a.

[0216] During the first step S10, the encoded signal is analyzed inorder to obtain the encoding passes for each block of the image of eachresolution level.

[0217] The distortion with respect to the original image generated bydeletion of encoding passes is not however known, but it is neverthelesspossible to calculate the distortion generated with respect to the casein which all the encoding passes are included in the signal.

[0218] The following step S11 provides for implementing arate/distortion allocation system such as that illustrated by thealgorithms of FIGS. 6a and 6 b and in which for each block thetruncation points are defined which are necessary to configure the finalbitstream.

[0219] Step S12 corresponds to the construction of the final bitstreamand provides a JPEG2000 image signal structured differently from thestarting image signal.

[0220]FIG. 6a illustrates an algorithm for determining a configurationof data of a digital signal of an image for a quality layer according tothe invention.

[0221] The algorithm comprises a plurality of steps or portions ofsoftware code corresponding to steps of the method according to theinvention and whose execution, for example, by the central processingunit 103 of the apparatus of FIG. 2, enables the method to beimplemented.

[0222] The computer program “Progr” which, as mentioned earlier, isstored, for example, in the memory 104 of the apparatus of FIG. 2, isbased on that algorithm and the execution of this program enables themethod according to the invention to be implemented.

[0223] Generally, the object of the algorithm of FIG. 6a is to determinea configuration of data of an image signal which is such that the signalin that configuration satisfies a quality mode desired by the user interms of data rate and is of acceptable visual quality for that user.

[0224] To achieve this, provision is made to determine the truncationpoints of the data blocks of the image signal which define the qualitylayer.

[0225] The algorithm commences with a first step S20 during which theresolution level R of the image signal is initialized to the maximumresolution R_(max) for the chosen display mode.

[0226] During the following step S21, provision is made for determininga minimum reduction in rate D_(min) desired as a function of a qualitymode desired by the user (for example the quality modes “Super Fine”,“Fine” and “Normal” of the JPEG standard).

[0227] This minimum reduction in rate is judged with respect to thetotal rate Dt of data conveyed by the entire image signal.

[0228] Later, in the description made with reference to FIG. 7, thepossible relationships of conversion between the quality modes “SuperFine”, “Fine” and “Normal” will be seen, and the correspondingreductions in rate.

[0229] During the following step illustrated by the reference S22, thealgorithm makes provision for determining the truncation points for eachdata block of the image signal.

[0230] It should be noted that it is perfectly possible to deal withonly certain blocks of the image.

[0231] As shown in FIG. 6a, that step divides up into the followingsteps S220 to S227.

[0232] During step S220, provision is made to classify the data blocksfor the resolution considered according to the values of distortionwhich is generated by the deletion in each block of a predeterminedmaximum number N of encoding passes.

[0233] The number N may vary from one resolution level to another.

[0234] The number N corresponds to a maximum number of encoding passesthat it is possible to delete for the data blocks in the resolutionlevel considered and for the quality mode considered, while preserving agiven visual quality that is acceptable to the user.

[0235] Thus, beyond that number, it is considered that the distortiongenerated by the deletion of encoding passes induces artifacts which arevisible in the final image, so adversely affecting its visual quality.

[0236] It is hence possible to configure the data of an image signal bydetermining the data (encoding passes) which it will later be possibleto delete taking into account that given number N.

[0237] The number N is, for example, obtained by trials on differenttypes of images which may be encountered in practice. The set of imagesused for those trials is sufficiently heterogeneous to representpractically all the possibilities encountered in practice, that is tosay for example images having a high or low degree of texture, or few ormany outlines. Beyond the fixed number N, even if the image viewed alonemay appear acceptable, a comparison with the original image enables theartifacts to be seen.

[0238] For example, the number N may be fixed empirically at 4 for themaximum resolution level and fixed at a lower level for the otherresolution levels. The number N could also be fixed after havingperformed tests on a set of images in order to reach a given mean valueof PSNR (Peak Signal to Noise Ratio), but the resulting visualimpression is then not always homogeneous.

[0239] It may also be envisaged to apply a maximum number N as afunction of different characteristics of the image signal which would beidentified beforehand.

[0240] In this example there would thus be a plurality of maximumnumbers N as a function of the type of image encountered.

[0241] The classification of the blocks for the resolution levelconsidered (S220) is based on the article entitled “Adaptive imagecoding based on the discrete wavelet transform”, by Jafarkhani,Farvardin and Lee, Proceedings, Int Conf. Image Proc., vol.3, pp343-347, Nov. 1994.

[0242] In that article, the classification is based on a criterion ofencoding gain.

[0243] According to the invention, the classification is implementedusing a different criterion which is that of the distortion generated bythe deletion of a fixed number, N, of encoding passes.

[0244] The object of this classification is to obtain classes of blockshaving the same statistical properties such that the distribution of theblocks into a class is consistent from the point of view of theencoding.

[0245] Consider the case of K blocks organized in terms of increasingvalue of their distortion d_(i), i=1,2, . . . , K which it is desired todistribute into two distinct classes. An integer K′ is sought such thatthe blocks from 1 to K′ belong to the first class and that the otherblocks belong to the second class. The mean m_(i) and the standarddeviation σ_(i) of the class i=1,2, . . . , K are defined by thefollowing relationships: $\begin{matrix}{m_{1} = {\frac{1}{K^{\prime}}{\sum\limits_{n = 1}^{K^{\prime}}d_{n}}}} \\{m_{2} = {\frac{1}{K - K^{\prime}}\quad {\sum\limits_{n = {K^{\prime} + 1}}^{K}d_{n}}}} \\{\sigma_{1}^{2} = {\frac{1}{K^{\prime}}\quad {\sum\limits_{n = 1}^{K^{\prime}}\left( {d_{n} - m_{1}} \right)^{2}}}} \\{\sigma_{2}^{2} = {\frac{1}{K - K^{\prime}}\quad {\sum\limits_{n = {K^{\prime} + 1}}^{K}\left( {d_{n} - m_{2}} \right)^{2}}}}\end{matrix}$

[0246] The integer K′ is chosen such that:

q ₁ =q ₂  (1)

[0247] $\begin{matrix}\begin{matrix}{where} & {q_{i} = \frac{\sigma_{i}}{m_{i}}}\end{matrix} & (2)\end{matrix}$

[0248] An iterative algorithm for finding the integer K′ satisfyingrelationship (1) or minimizing |q₁−q₂| is described below with referenceto FIG. 6b, that algorithm also forming part of the algorithm of FIG.6a. The symbol |x| represents the absolute value of x.

[0249] Step S2200 of FIG. 6b makes provision for initializing theiteration value i and the value K′. For example K′=K/2 may be set.

[0250] The step S2201 makes provision for calculating q₁ and q₂ by usingrelationship (2) and by incrementing the iteration value by one uniti=i+1.

[0251] Step S2202 is a test step during which it is determined whether$\frac{{q_{1} - q_{2}}}{q_{1}} < \delta$

[0252] or whether i>i_(max).

[0253] Where the result is affirmative, for either one of these cases,the classification is terminated.

[0254] Otherwise the value of K′ is updated according to the result ofstep S2203 in the following manner:

[0255] if q₁<q₂ step S2204 is proceeded to, during the course of whichthe value of K′ is given by the equation: K′=K′+ΔK′.

[0256] if (R_(i) ^(n),D_(i) ^(n)) step S2205 is proceeded to, during thecourse of which the value of K′ is given by the equation: K′=K′−ΔK′.

[0257] The step S2201 already described above is then executed again.

[0258] For a distribution into a number of classes M>2, calculation mustbe made of M quotients ${q_{i} = \frac{\sigma_{i}}{m_{i}}},$

[0259] with i=1,2, . . . , M.

[0260] The algorithm stops when$\frac{{\max_{i}q_{i}} - {\min_{i}q_{i}}}{\min_{i}q_{i}} < \delta$

[0261] max_(i)q_(i) or when the number of iterations exceeds i_(max),where max_(i)q_(i) is the maximum value of q_(i) and min_(i)q_(i) is theminimum value of q_(i) for i=1,2, . . . , M.

[0262] At each loop the number of blocks for the classes correspondingto q_(i) maximum and minimum are adjusted such that the values q_(i) areas close as possible to each other.

[0263] When the algorithm of FIG. 6b has terminated and thus when theclassifying step 220 of FIG. 6a has terminated, there are, for example,three classes of blocks having equivalent statistical properties interms of standard deviation/mean ratio and reflecting the distortiongenerated by the deletion of a predetermined maximum number N ofencoding passes.

[0264] During the following step S221, provision is made forinitializing the truncation points (portions of binary elements) of thebitstream of the coefficients of each block of coefficients of theresolution level considered.

[0265] Three values of truncation points t0(i), t1(i), t2(i) are thusprovided which each correspond to the three classes of blocks mentionedearlier. Thus, for example, it is possible to set the followingtruncation point values for the maximum resolution level R₂ and for thequality mode “Fine”:

t 0(0)=0, t 1(0)=0, t 2(0)=1

t 0(1)=0, t 1(0)=1, t 2(2)=1

.

.

.

t 0(i _(max))=1, t 1(i _(max))=3, t 2(i _(max))=4 with i _(max)=6 andt(i)≦N.

[0266] The above represents the different values of truncation pointsfor the classes of blocks considered as the loop index i of thealgorithm of FIG. 6a increments.

[0267] It will be noted that when the value of the truncation pointindicates 0, it means that no encoding pass has been deleted whereas,when it indicates the value 1, it means that one encoding pass has beendeleted.

[0268] It will be noted that the truncation point values indicated bythe reference t0(i) correspond to the data blocks classified in a firstclass for which the blocks generate relatively high distortion valueswhen certain of the data constituting those blocks are not included inthe bitstream.

[0269] Consequently, low truncation values are applied to those blocks,which means that it is provided to delete few encoding passes for thoseblocks.

[0270] On the other hand, the truncation point values located by thereference t2(i) are allocated to blocks classified in the third classwhich generate the least distortion with respect to the blocks of theother classes when data constituting those blocks are deleted from them.

[0271] Due to this, for those blocks it is possible to delete moreencoding passes than for the blocks belonging to the first class.

[0272] Thus, within the same resolution level, the quantity of data(number of encoding passes) to be deleted from the blocks present inthat resolution level is distributed as a function of the data blocksthemselves.

[0273] During step S221, determination is made of a number m of encodingpasses (portions of binary elements of the coefficients of the blocks ofa particular resolution level) to be deleted from the signal as afunction of a given maximum number N which guarantees a given visualquality.

[0274] The number N thus corresponds to the maximum number of encodingpasses which it is possible to delete without degrading the visualquality of the image.

[0275] It has been seen already how the number N can be determined.

[0276] It will be remarked that the number N may vary from one class ofblocks to the other and also, for the same class, from one resolutionlevel to another.

[0277] It will be noted that the truncation point values of thebitstream of a block which were given above are determined as a functionof the number N which is specific to each class of blocks.

[0278] It will thus be seen that the number N, equal to 4 for example,is only applicable for one of the classes of blocks, i.e. the blockswhich generate the least distortion.

[0279] Taking into account the number of encoding passes which it ispossible to delete for each data block in the resolution considered,determination is made during the following step S222 of the reduction inrate D_(i) generated by the deletion of the encoding passes definedbeforehand at step S221.

[0280] During that same step, the reduction in rate D_(i) is incrementedfor the resolution level considered by adding to it the possiblereduction in rate which may have been determined for the resolutionlevel immediately above.

[0281] In the example described, the loop performed at step S22 for themoment only concerns the resolution level R_(max) (e.g. R₂) and thusthere is no reduction in rate for a resolution level immediately above.

[0282] During the following step S223, the rate reduction, incrementedif need be with the possible prior rate reduction values, is compared tothe minimum rate reduction desired D_(min) of step S21.

[0283] As a function of the result of the comparison, a decision istaken as to whether to reiterate at least certain of the previous stepsfor the current resolution level or for the level below (deletion ofadditional encoding passes), or whether the desired data configuration(rate, visual quality) has been determined.

[0284] Thus, if the rate reduction determined at step S222 is greaterthan D_(min), that means that the encoding passes which have beenproposed for deletion are sufficient to obtain a rate reduction that issatisfactory for the user. The guarantee of obtaining an acceptablevisual quality for the user is obtained during step S221 through thechoice of the maximum number of encoding passes which it is possible todelete for each class of blocks.

[0285] For the resolution levels which have not been taken into accountduring step S22, all the encoding passes of the blocks of thoseresolution levels will therefore be included in the quality layer thuscreated.

[0286] It will be noted that determining the number m of encoding passesto delete for a given quality layer for the resolution level consideredin a way amounts to determining a number n of encoding passes to keep inthe quality layer, these encoding passes defining the data of the blocksconstituting a quality layer of the signal.

[0287] A configuration of the data of the digital image signal is thusdetermined.

[0288] The user can then select one of the quality modes of that dataconfiguration which is present in the signal by deleting thesupplementary data (encoding passes defined at step S221), that is tosay by deleting a given number of quality layers.

[0289] Consecutively to step S223, the following step S3 makes provisionfor constructing the image signal in accordance with the JPEG2000standard as illustrated in FIG. 5a.

[0290] On the contrary, when the rate reduction (cumulated with thepossible rate reductions of the higher resolutions) mentioned at stepS222 is less than D_(min), the rate reduction obtained is not sufficientand other encoding passes must be deleted if possible.

[0291] To do that, a test is provided at the following step S224 inorder to determine whether the value of the truncation points can beincreased in the resolution considered.

[0292] If i is less than i_(max), the following step S225 makesprovision for incrementing the loop index i by one unit and forallocating new values to the values of the truncation points t0(i),t1(i) and t2(i) as defined earlier so as to not to exceed the maximumnumber No.

[0293] Step S222 already described above is then executed again todetermine the rate reduction generated by the deletion of the encodingpasses newly determined at step S225.

[0294] If need be, as already mentioned above, the rate reductiongenerated may possibly be increased by the rate reduction which may havebeen determined beforehand at one or more of the higher resolutionlevels.

[0295] The following step S223 already described above is then executedagain.

[0296] When the result of the test made at step S224 is negative, itmeans that it is no longer possible to delete encoding passes for theresolution level considered on account of the threshold N guaranteeing agiven visual quality for the signal in the resolution considered.

[0297] In that case, step S224 is followed by a step S226 which providesfor carrying out another test on the value of the current resolutionlevel in order to determine whether it is the last for the image signalconsidered.

[0298] If the current resolution is the last resolution, i.e. resolutionR₀, it means that despite all the encoding passes which it has beenpossible to delete for all the higher resolution levels, taking intoaccount the maximum truncation values for each resolution level (numberN), the rate reduction is nevertheless still less than the desired ratereduction D_(min).

[0299] However, it is no longer possible in this case to delete otherencoding passes if it is desired to ensure a good visual quality for theimage signal.

[0300] It will however be noted that the trials which it has beenpossible to perform show that in such cases (if the N values have beenset as indicated above), rate reductions are nevertheless obtained whichare very close to the minimum rate reduction desired.

[0301] Step S226 is then followed by step S3 which has already beendescribed above.

[0302] When the result of the test carried out at step S226 is negative,that step is followed by a step S227 which makes provision fordetermining, for the loop of step S22, the truncations of the blocks ofthe resolution level R-1 immediately below.

[0303] Step S227 is then followed by step S220, already described aboveduring which the data blocks of the resolution level considered areclassified, for example, into three classes according to the distortionvalues generated.

[0304] The following steps which have already been described above arethen executed again. It will thus be noted that, so long as thecumulative rate reduction remains less than the minimum rate reductiondesired, and so long as it can still be envisaged to delete encodingpasses in the current resolution level, or even in the resolution levelhierarchically below, the execution of the algorithm continues in orderto seek further encoding passes to delete.

[0305] By virtue of the presence of the threshold N which ensures thevisual quality of the image signal in the resolution considered, it isnot possible to delete too many encoding passes in a resolution levelconsidered.

[0306] Thus the invention advantageously makes it possible to distributethe deletion of encoding passes in different resolution levels in orderto guarantee a visual quality that is acceptable to the user.

[0307] As was seen earlier, the distribution of rate is furthermore notperformed in a haphazard manner within a particular resolution level,since account is taken of the type of data block, and in particular ofwhether it belongs to a particular class, in order to delete a number ofencoding passes which is adopted for the block considered.

[0308] It will be noted that the user of a digital camera has thepossibility of determining the quality mode before taking hisphotograph. A different quantization step size (used in circuit 22 ofFIG. 1) corresponds to each quality mode and the encoding passes arethen all included in the final bitstream.

[0309] By virtue of the configuration of the data of the signalaccording to the invention, the user can also reduce the quality modeand/or resolution after having stored the photograph, and so free somememory.

[0310] There are thus a plurality of possible cases according to theoriginal quality mode of the image signal and the quality mode desiredby the user.

[0311]FIG. 7 summarizes the possibilities for conversion betweendifferent quality modes defined by the JPEG standard and specifies acorresponding rate reduction which can be used on implementing theinvention.

[0312] In the case of an original compression in “Super Fine” mode, itis desired to convert the image into “Fine” mode or “Normal” mode. 20%and 40% of the maximum size of the image (i.e. of the image in “SuperFine” mode) can then respectively be taken as the rate reduction.

[0313] In the case of an original compression in “Fine” mode, it isdesired to convert the image into “Normal” mode. 25% of the maximum sizeof the image (i.e. of the image in “Fine” mode) can then be taken as therate reduction.

[0314] In the case of a original compression in “Normal” mode, noconversion is possible.

[0315] It should be noted that the aforementioned quality modes eachcorrespond to a quality layer created in the signal.

[0316]FIG. 8 gives a simplified illustration of the configuration of thesignal obtained by resolution level if the algorithm of FIG. 6a isapplied several times for a JPEG2000 image signal compressed in “SuperFine” mode for the upper resolution level R₂ and which it is desired toconvert into “Fine” and “Normal” mode for that resolution.

[0317] For each resolution the encoding passes to include or not in thebitstream are represented: the encoding passes above a limit F, forexample, represent the encoding passes to delete in order to obtain the“Fine” quality mode (this also defines a corresponding quality layer inthe signal).

[0318] For the “Super Fine” quality mode, all the encoding passes areincluded in the final bitstream and thus the limits SF correspond to100% of encoding passes included for each resolution level.

[0319] For the “Fine” quality mode, the configuration of the signal inthe most complex case has been represented.

[0320] Thus the truncation points have been applied progressively forthe upper resolution level R₂ up to their maximum values (guaranteeingthe preservation of a given visual quality), which corresponds to theloop constituted by steps S222-S223-S224-S225 of FIG. 6a.

[0321] However, as the rate reduction was insufficient (step S223),truncation points were applied to resolution R₁, here too up to theirmaximum values, nevertheless without obtaining a sufficient ratereduction. Thus truncation points were then applied for the resolutionR₀, which corresponds to the loop constituted by steps S226, S227, andS220 to S225 of FIG. 6a.

[0322] Thus, for example, the contribution of each resolution level tothe rate reduction for resolution R₂ when passing from “Super Fine” modeto “Fine” mode corresponds for levels R₂, R₁ and R₀ respectively to 7%,9% and 5% of encoding passes deleted with respect to the total number ofencoding passes in the signal for the maximum resolution level.

[0323] For the “Normal” quality mode, the configuration of the signal inthe most complex case has also been represented and the same descriptioncan thus also be used for the “Fine” mode.

[0324] In order to be able to convert an image in a quality mode, forexample “Fine”, to a lower quality mode, for example “Normal”, it isnecessary for all the encoding passes of the “Normal” mode to be alsoincluded in the “Fine” mode. In FIG. 8 this results in the fact that thelimits for the “Normal” mode must be below the limits for the “Fine”mode whatever the resolution considered.

[0325] Thus, in step S221 of FIG. 6a, for a given quality, the value ofthe truncation points applied for the quality above, i.e. the number ofencoding passes rejected for the quality mode above, must be set as theinitial value for the truncation points, that is to say as the minimumnumber of encoding passes rejected.

[0326]FIGS. 9a and 9 b represent a particular configuration of aJPEG2000 image signal which can be obtained by the algorithm of FIGS. 6aand 6 b and illustrates the problem of the conversion from one qualitymode to another when it is also desired to reduce the size of the imageby deleting a resolution.

[0327] In the view on the left, FIG. 9a represents the projection of animage into the different frequency sub-bands after having applied awavelet transform to the image, and, in the view on the right,represents the configuration which can be obtained on implementing theinvention.

[0328] It is assumed here that the image has large wavelet coefficientsin the upper resolution R₂ and that the truncation points applied inthat resolution are sufficient to obtain a satisfactory rate reductionfor the “Fine” and “Normal” quality modes. Two quality layers (Fand N)are thus created for the maximum resolution R₂. For the lowerresolutions all the blocks will thus be included, whatever the qualitymode (“Super Fine”, “Fine” and “Normal”).

[0329]FIG. 9b repeats the views of FIG. 9a when the upper resolution isdeleted, that is to say when the user changes the size of the image, forexample, to free up memory space and take additional photographs. Thequality modes, as they have been defined, are then no longer accessiblefor resolution R₁: it is not possible for the user to reduce the qualityof the image if he desires to gain further memory space.

[0330] This particular case is an extreme case in which the conversionis not possible in the lower resolutions.

[0331] This is because, in the more general case illustrated in FIG. 8,the rate reduction is determined on the basis of the total data rate ofthe image in the upper resolution level and, consequently, it is notknown what rate reduction would be obtained on passing from an image in“Super Fine” mode in resolution R₁ to an image in “Fine” mode inresolution R₁.

[0332] The configuration presented in FIG. 8 thus remains valid only ifthe image is kept at full resolution.

[0333] If, on the contrary, it is desired to enable the resolution ofthe image to be reduced while keeping each quality mode, the rate/visualquality allocation system illustrated in FIGS. 6a and 6 b must beapplied determining the appropriate rate reduction for each possibledisplay resolution R_(a).

[0334]FIG. 10 repeats the algorithm of FIG. 6a by performing a loop onthe display resolution R_(a) in order to allow the conversion from agiven quality mode to a lower quality mode whatever the resolutionchosen.

[0335] It will be noted that to decode an image at a display resolutionR_(a) all the resolution levels less than or equal to R_(a) are needed.

[0336] Thus a minimum rate reduction is determined for each resolutionlevel considered and the data of the signal will be configured for eachresolution level in one or more quality layers.

[0337] A first step S30 initializes the display resolution R_(a), set tothe maximum resolution R_(max) of the image.

[0338] During the following step S31, the minimum desired rate reductionD_(min)(R_(a)) is determined as a function of the quality mode Q desiredby the user and of the total data rate D_(t) obtained when all theencoding passes of the image are included in the bitstream for thedisplay resolution R_(a) considered.

[0339] The following step S32 initializes the resolution R to thedisplay resolution R_(a).

[0340] The following step S33 determines the truncation points for eachblock of the image for the resolution R considered. That step isidentical to step S22 of FIGS. 6a and 6 b and will thus not be givenhere.

[0341] During that step, the rate reduction determined for the currentresolution is compared to D_(min)(R_(a)) and, as a function of theresult of the comparison, it is decided either that the preceding stepsmust be repeated for that resolution (deletion of a greater number ofencoding passes for that resolution), or that it is necessary to deleteencoding passes in the lower resolution levels for that quality layerand that rate reduction, or that it is necessary to reiterate steps S31and S32 for the lower resolution levels, or that the desiredconfiguration (all quality layers) has been obtained for thatresolution.

[0342] Step S34 is a test during which it is determined whether thedisplay resolution R_(a) is the last resolution to process.

[0343] According to the case envisaged, the last resolution to processmay be the last resolution of the signal or a predetermined resolutionbeyond which it is not desired to go.

[0344] If it is the last resolution, step S4 is proceeded to in order toconstruct the final bitstream.

[0345] Otherwise, step S35 is proceeded to which provides for applyingthe algorithm to the display resolution R_(a)=R_(a)−1. After that step,step S31 is looped back to in order to determine the rate reductionnecessary for that new display resolution as already described above.

[0346] That algorithm enables the user to delete a resolution (forexample R₂) as in FIG. 9 and furthermore to have access, in theremaining lower resolutions, to one or more different quality modes(quality layers created).

[0347]FIG. 11 illustrates a configuration obtained by applying thealgorithm of FIG. 10, for an original JPEG2000 image signal compressedin “Super Fine” quality mode, in full resolution R₂, and which it isdesired to convert into “Fine” and “Normal” mode, whatever the chosenresolution.

[0348] For each resolution the encoding passes to include or not in thebitstream are represented. The truncation points for obtaining the“Fine” and “Normal” modes at full resolution are indicated in thicklines. The truncation points for obtaining the “Fine” and “Normal” modesat resolution R₁ are indicated in dashed lines and in italic. Thetruncation points for obtaining the “Fine” and “Normal” modes atresolution R₀ are indicated in fine lines.

[0349] For the “Super Fine” quality mode, all the encoding passes areincluded in the final bitstream (upper quality layer) and thus thelimits SF correspond to 100% of encoding passes included for eachresolution level. For the other modes, the general case applies, that isto say that to obtain a desired rate reduction, the truncation points(quality layer(s) hierarchically below) are applied in the displayresolutions and in the resolutions below.

[0350] As already mentioned above in the description for FIG. 8, inorder to be able to convert an image in a quality mode, for example“Fine”, to a lower quality mode, for example “Normal”, while preservingthe same display resolution, it is necessary for all the encoding passesof the “Normal” mode to be also present in the “Fine” mode. The resultof this in FIG. 11 is that the limits corresponding to “Normal” mode(for example, N(R₂) in each resolution level must be situated below thelimits for “Fine” mode (for example F(R₂)) in each resolution levelwhatever the resolution considered.

[0351] Similarly, it is desired to be able to delete a resolution whilepreserving a given quality.

[0352] If it is wished, for example, to pass from “Fine” mode at fullresolution (F(R₂)) to “Fine” mode at lower resolution (F(R₁)), it isnecessary for the encoding passes of the “Fine” mode of the lowerresolution to be present in the “Fine” mode at full resolution. In FIG.11 this results in the fact that for a given quality mode, the limitscorresponding to the higher display resolutions F(R₂) are situated abovethe limits corresponding to the lower display resolutions (F(R₁),F(R₀)).

[0353] It should be noted that at step S221 of FIG. 6a, for a givendisplay resolution and quality mode, the initial value of the truncationpoints must be fixed as:

[0354] the value of the truncation points applied for the quality modeabove if the display resolution processed is full resolution,

[0355] otherwise, the maximum value between:

[0356] the value of the truncation points of the same quality mode butfor a higher display resolution.

[0357] the value of the truncation points of the quality mode above butfor the same display resolution.

[0358]FIG. 12 illustrates a configuration obtained by applying thealgorithm of FIG. 10, for an original JPEG2000 image signal compressedin “Fine” quality mode, in full resolution R2, and which it is desiredto convert into “Normal” mode, whatever the chosen resolution.

[0359] The truncation points for obtaining the “Normal” mode at fullresolution (N(R₂)) are indicated in thick lines. The truncation pointsfor obtaining the “Normal” mode at resolution R₁ (N(R₁)) are indicatedin dashed lines and in italic. The truncation points for obtaining the“Normal” mode at resolution R₀ (N(R₀)) are indicated in fine lines.

[0360] For the “Fine” quality mode (highest quality layer), all theencoding passes are included in the final bitstream and the limits Fthus correspond to 100% of encoding passes included, for each resolutionlevel.

[0361] As for FIG. 11, for the other quality modes, the general caseapplies, that is to say that to obtain a desired rate reduction, thetruncation points (quality layer(s) hierarchically below) are applied inthe display resolutions and in the resolutions below.

[0362]FIGS. 13a and 13 b repeat the example illustrated in FIGS. 9aand 9b (deletion of a resolution level), but with the algorithm of FIG. 10.This Figures show the possibility of converting a signal from onequality mode to a lower quality mode whatever the display resolutionchosen.

[0363] In the view on the left, FIG. 13a represents the projection of animage into the different frequency sub-bands after having applied awavelet transform to the image, and, in the view on the right,represents the configuration which can be obtained on applying thealgorithm of FIG. 10.

[0364] It is assumed here that the image has high wavelet coefficientsin the highest resolution R₂ and that truncation points applied in thatresolution are sufficient to obtain a satisfactory rate reduction forthe “Fine” and “Normal” quality modes and for a display at fullresolution (two quality layers F(R₂) and N(R₂) are thus created in asingle resolution level).

[0365] For the lower resolutions all the blocks will thus be included,whatever the quality mode.

[0366] For a display at resolution R_(a)=R₁, the truncation points arerepresented in dashed lines.

[0367] It is assumed here that the general case applies, that is to saythat truncation points must be applied in the resolutions R₁ and R₀ toobtain the quality modes “Fine” and “Normal”.

[0368]FIG. 13b repeats the views of FIG. 13a when the upper resolutionis deleted, that is to say when the user changes the size of the image,for example, to free up memory space and take additional photographs.

[0369] In that image of reduced size, it is also possible to convert theimage into “Fine” mode F(R₁) by applying the corresponding truncationpoints to a display at resolution R₁.

[0370] In the description made with reference to FIGS. 8 and 11, therelationships between the different quality modes for a given displayresolution (“Super Fine” quality mode above “Fine”, itself above“Normal”) and, for the same quality mode, the relationships between thedifferent display resolutions (highest display resolution above thelower display resolutions for a given quality).

[0371] Nevertheless, several other ways of organizing the bitstream canalso be envisaged.

[0372]FIGS. 14a and 14 b thus represent two possible configurations forresolution R₁.

[0373] To be able to simply convert an image to the desired quality modeand resolution, additional data must be added on the order of thequality modes. These data may be included in the compressed JPEG2000file, for example, in the segments corresponding to the markers denotedCOM (for comment), for each different tile of the image signal.

[0374] The order of the quality layers is thus added. It should be notedthat the “Super Fine” modes are not specified since, in all cases, theyinclude all the blocks of the desired resolution. For example for FIG.14a, the information will be of the type: [N0, N1, N2, F0, F1, F2].

[0375] This is because, in the case of FIG. 14a, the quality modescorrespond to quality layers within the meaning of the JPEG2000standard, that is to say that each quality mode corresponds toadditional data in one or more resolutions. There are thus the followingquality layers:

[0376] N(R0) adds information in R₀,

[0377] N(R1) adds information in R₀ and R₁,

[0378] N(R2) adds information in R₀, R₁ and R₂,

[0379] F(R0) adds information in R₀,

[0380] F(R1) adds information in R₀ and R₁,

[0381] F(R2) adds information in R₀, R₁ and R₂,

[0382] SF(R2) adds information in R₀, R₁ and R₂.

[0383] This organization is possible since the same ordering of thequality modes is present in each resolution.

[0384] In contrast, in the case of FIG. 14b, the ordering is differentin resolution R₀ and in resolution R₁: thus in R₀ we have F(R₁) aboveN(R₂) and in R₁ we have N(R₂) above F(R₁).

[0385] It is thus not possible to define the quality modes in terms ofprogressive layers, since that would then give:

[0386] N(R₀) adds information in R₀,

[0387] N(R₁) adds information in R₀ and R₁,

[0388] N(R₂) adds information in R₀, R₁ and R₂,

[0389] F(R₀) adds information in R₀,

[0390] F(R₁) adds information in R₀ and information in R₁ is deleted.

[0391] This situation is not compatible with the quality layerdefinition of the JPEG2000 standard where each layer must includeinformation. Quality layers are thus defined for each resolution, which,in the example considered, gives 15 layers (7 layers for resolution R₀,5 for R₁ and 3 for R₂) and the additional information contained in thesegments corresponding to the marker COM enable it to be determinedwhich layers must be included in order to reconstruct a new JPEG2000file at a given quality and level.

[0392] In a way, information is added to the signal to establish acorrespondence between the quality layers and the quality modes since,in fact, when the quality layers of the compressed signal are decoded,it is not known what they correspond to. Nevertheless, no additionalcalculation will be necessary.

[0393] Thus a decodable image signal is preserved whatever the decoder.

[0394] It will be noted that, generally, the configuration of data of adigital signal according to the invention can also be implemented ontranscoding that signal.

1. A method of determining a data configuration of a digital signal ofan image, the signal having undergone at least one spatio-temporaltransformation in at least one resolution level, characterized in thatthe method comprises the following steps: determining at least oneminimum rate reduction (D_(min)) with respect to the total data rate ofat least one resolution level of the signal, as a function of a qualitymode desired for the signal, configuring the data of the signal in atleast one quality layer defined for at least one resolution level of thesignal such that said at least one quality layer so defined correspondsto a given visual quality of the signal, the data making up that atleast one quality layer being obtained by a reduction (D) of the totalrate of the data of said at least one resolution level of the signalwhich is greater than or equal to the minimum reduction (D_(min)).
 2. Amethod according to claim 1, characterized in that the signal issuingfrom said at least one spatio-temporal transformation comprises blockseach containing at least one transformed coefficient having the form ofa series of binary elements, the data making up a quality layer which isdefined in at least one resolution level of the signal, corresponding,for at least one block of a given resolution level, to at least a numbern of portions of binary elements of said at least one block.
 3. A methodaccording to claim 2, characterized in that said at least one number nof portions of binary elements is determined as a function of a givennumber N which corresponds to the maximum number of portions of binaryelements which it is possible to delete in a block to obtain a givenvisual quality in the resolution considered.
 4. A method according toclaim 3, characterized in that the method comprises a step ofclassifying the data blocks as a function of the values of thedistortion which is generated for each block when a given number ofportions of binary elements is deleted from each block.
 5. A methodaccording to claim 4, characterized in that the data blocks areclassified into different classes of blocks to each of which belong thedata blocks having given rise to values of distortion which areconsistent with each other.
 6. A method according to claim 4 or 5,characterized in that the maximum number N of portions of binaryelements which it is possible to delete from a data block depends on theclassification of that block.
 7. A method according to claim 1,characterized in that the signal issuing from said at least onespatio-temporal transformation comprises transformed coefficientsgrouped into blocks in which each coefficient is quantized over aplurality of bits, each bitplane of a block being encoded by a pluralityof encoding passes which each provides a portion of the encoding datafor the block considered, configuring the data of the signal in at leastone quality layer comprising obtaining, in at least one resolution levelof the signal and for each of the blocks considered, a minimum number mof encoding passes corresponding to the given visual quality.
 8. Amethod according to claim 7, characterized in that the number m isobtained as a function of a maximum given number N of encoding passeswhich it is possible to delete for the coefficients of a data block inorder to obtain a given visual quality in the resolution considered. 9.A method of determining a data configuration of a digital signal of animage, the signal having undergone at least one spatio-temporaltransformation in at least one resolution level, characterized in thatthe method comprises the following steps: determining at least oneminimum rate reduction (D_(min)) with respect to the total data rate ofat least one resolution level of the signal, as a function of a qualitymode desired for the signal, distributing, over at least certain of theresolution levels of the signal, a rate reduction (D) greater than orequal to (D_(min)) and which is such that the reduction in data ratedistributed in each resolution level is less than or equal to athreshold representing a given visual quality.
 10. A method ofdetermining a data configuration of a digital signal of an image, thesignal having undergone at least one spatio-temporal transformation inat least one resolution level, thus providing transformed coefficientseach taking the form of a series of binary elements comprising aplurality of portions, characterized in that the method comprises thefollowing steps: i) determining at least one minimum rate reduction(D_(min)) with respect to the total data rate of at least one resolutionlevel of the signal, as a function of a quality mode desired for thesignal, ii) determining, for a given resolution level (R=R_(i)) and forat least certain transformed coefficients of that level, a number mwhich may vary from one coefficient to another, of portions of binaryelements to delete from the signal, with m≦N, where N is a maximum givennumber which guarantees a given visual quality in the resolution levelconsidered, iii) determining the reduction in rate (D_(i)) generated bythe deletion in the resolution level (R) of the m portions of binaryelements of said at least certain transformed coefficients, iv)comparing the rate reduction added to the possible rate reductiondetermined for the resolution level hierarchically above with respect tothe minimum rate reduction (D_(min)), v) as a function of the result ofthe comparison, deciding as to the reiteration of steps ii) to v) forthe resolution level R or for the resolution level below (R=R_(i-1)) oras to the determined data configuration.
 11. A method of determining adata configuration of a digital signal of an image, the signal havingundergone at least one spatio-temporal transformation in at least oneresolution level, thus providing transformed coefficients each takingthe form of a series of binary elements comprising a plurality ofportions, characterized in that the method comprises the followingsteps: i) determining at least one minimum rate reduction (D_(min)) withrespect to the total rate of a display resolution level R_(a) as afunction of a quality mode desired for the signal, ii) determining, fora resolution level R_(i) which corresponds initially to R_(a) and for atleast certain transformed coefficients of that level, a number m whichmay vary from one coefficient to another, of portions of binary elementsto delete from the signal, with m≦N, where N is a maximum given numberwhich guarantees a given visual quality in the resolution levelconsidered, iii) determining the reduction in rate (D_(i)) generated bythe deletion in the resolution level (R_(i)) of the m portions of binaryelements of said at least certain transformed coefficients, iv)comparing the reduction in rate with respect to the minimum ratereduction (D_(min)), v) as a function of the result of the comparison,deciding as to the reiteration of steps ii) to v) for the resolutionlevel (R_(i)) or for the resolution level hierarchically below(R_(i)=R_(i)−1) or as to the reiteration of steps i) to v) for the levelof display resolution hierarchically below (R_(a)=R_(a)−1) or as to thedetermined data configuration.
 12. A device for determining-a dataconfiguration of a digital signal of an image, the signal havingundergone at least one spatio-temporal transformation in at least oneresolution level, characterized in that the device comprises: means fordetermining at least one minimum rate reduction (D_(min)) with respectto the total rate of data of at least one resolution level of thesignal, as a function of a quality mode desired for the signal, meansfor configuring the data of the signal in at least one quality layerdefined for at least one resolution level of the signal such that saidat least one quality layer so defined corresponds to a given visualquality of the signal, the data making up that at least one qualitylayer being obtained by a reduction (D) of the total rate of the data ofsaid at least one resolution level of the signal which is greater thanor equal to the minimum reduction (D_(min)).
 13. A device according toclaim 12, characterized in that the signal issuing from said at leastone spatio-temporal transformation comprises blocks each containing atleast one transformed coefficient having the form of a series of binaryelements, the data making up a quality layer which is defined in atleast one resolution level of the signal, corresponding, for at leastone block of a given resolution level, to at least a number n ofportions of binary elements of said at least one block.
 14. A deviceaccording to claim 13, characterized in that said at least one number nof portions of binary elements is determined as a function of a givennumber N which corresponds to the maximum number of portions of binaryelements which it is possible to delete in a block to obtain a givenvisual quality in the resolution considered.
 15. A device according toclaim 14, characterized in that the device comprises means forclassifying the data blocks as a function of the values of thedistortion which is generated for each block when a given number ofportions of binary elements is deleted from each block.
 16. A deviceaccording to claim 12, characterized in that the signal issuing fromsaid at least one spatio-temporal transformation comprises transformedcoefficients grouped into blocks in which each coefficient is quantizedover a plurality of bits, each bitplane of a block being encoded by aplurality of encoding passes which each provides a portion of theencoding data for the block considered, means for configuring the dataof the signal in at least one quality layer comprising means forobtaining, in at least one resolution level of the signal and for eachof the blocks considered, a minimum number m of encoding passescorresponding to the given visual quality.
 17. A device according toclaim 16, characterized in that the number m is obtained as a functionof a maximum given number N of encoding passes which it is possible todelete for the coefficients of a data block in order to obtain a givenvisual quality in the resolution considered.
 18. A device fordetermining a data configuration of a digital signal of an image, thesignal having undergone at least one spatio-temporal transformation inat least one resolution level, characterized in that the devicecomprises: means for determining at least one minimum rate reduction(D_(min)) with respect to the total rate of data of at least oneresolution level of the signal, as a function of a quality mode desiredfor the signal, means for distributing, over at least certain of theresolution levels of the signal, a rate reduction (D) greater than orequal to (D_(min)) and which is such that the reduction in data ratedistributed in each resolution level is less than or equal to athreshold representing a given visual quality.
 19. A device fordetermining a data configuration of a digital signal of an image, thesignal having undergone at least one spatio-temporal transformation inat least one resolution level, thus providing transformed coefficientseach taking the form of a series of binary elements comprising aplurality of portions, characterized in that the device comprises: meansfor determining at least one minimum rate reduction (D_(min)) withrespect to the total rate of data of at least one resolution level ofthe signal, as a function of a quality mode desired for the signal,means for determining, for a given resolution level (R=R_(i)) and for atleast certain transformed coefficients of that level, a number m, whichmay vary from one coefficient to another, of portions of binary elementsto delete from the signal, with m≦N, where N is a maximum given numberwhich guarantees a given visual quality in the resolution levelconsidered, means for determining the reduction in rate (D_(i))generated by the deletion in the resolution level (R) of the m portionsof binary elements of said at least certain transformed coefficients,means for comparing the rate reduction added to the possible ratereduction determined for the resolution level hierarchically above withrespect to the minimum rate reduction (D_(min)), means for deciding asto the determined configuration of data, as a function of the result ofthe comparison.
 20. A device for determining a data configuration of adigital signal of an image, the signal having undergone at least onespatio-temporal transformation in at least one resolution level,characterized in that the device comprises: means for determining atleast one minimum rate reduction (D_(min)) with respect to the totalrate of a display resolution level R_(a) as a function of a quality modedesired for the signal, means for determining, for a resolution levelR_(i) which corresponds initially to R_(a) and for at least certaintransformed coefficients of that level, a number m which may vary fromone coefficient to another, of portions of binary elements to deletefrom the signal, with m≦N, where N is a maximum given number whichguarantees a given visual quality in the resolution level considered,means for determining the reduction in rate (D_(i)) generated by thedeletion in the resolution level (R_(i)) of the m portions of binaryelements of said at least certain transformed coefficients, means forcomparing the reduction in rate with respect to the minimum ratereduction (D_(min)), means for deciding as to the configuration of thedata as a function of the result of the comparison.
 21. A digital cameracomprising a device according to one of claims 12 to
 17. 22. A digitalcamera comprising a device according to claim
 18. 23. A digital cameracomprising a device according to claim
 19. 24. A digital cameracomprising a device according to claim
 20. 25. An information storagemeans which can be read by a computer or a microprocessor containingcode instructions of a computer program for executing the steps of themethod according to one of claims 1 to
 8. 26. An information storagemeans which can be read by a computer or a microprocessor containingcode instructions of a computer program for executing the steps of themethod according to claim
 9. 27. An information storage means which canbe read by a computer or a microprocessor containing code instructionsof a computer program for executing the steps of the method according toclaim
 10. 28. An information storage means which can be read by acomputer or a microprocessor containing code instructions of a computerprogram for executing the steps of the method according to claim
 11. 29.A partially or totally removable information storage means which can beread by a computer or a microprocessor containing code instructions of acomputer program for executing the steps of the method according to oneof claims 1 to
 8. 30. A partially or totally removable informationstorage means which can be read by a computer or a microprocessorcontaining code instructions of a computer program for executing thesteps of the method according to claim
 9. 31. A partially or totallyremovable information storage means which can be read by a computer or amicroprocessor containing code instructions of a computer program forexecuting the steps of the method according to claim
 10. 32. A partiallyor totally removable information storage means which can be read by acomputer or a microprocessor containing code instructions of a computerprogram for executing the steps of the method according to claim
 11. 33.A computer program loadable onto a programmable apparatus, comprisingsequences of instructions or portions of software code for implementingthe steps of the method according to one of claims 1 to 8, when saidcomputer program is loaded and executed by the programmable apparatus.34. A computer program loadable onto a programmable apparatus,comprising sequences of instructions or portions of software code forimplementing the steps of the method according to claim 9, when saidcomputer program is loaded and executed by the programmable apparatus.35. A computer program loadable onto a programmable apparatus,comprising sequences of instructions or portions of software code forimplementing the steps of the method according to claim 10, when saidcomputer program is loaded and executed by the programmable apparatus.36. A computer program loadable onto a programmable apparatus,comprising sequences of instructions or portions of software code forimplementing the steps of the method according to claim 11, when saidcomputer program is loaded and executed by the programmable apparatus.